1. The Field of the Invention
This invention relates generally to computer graphics systems. More specifically, the present invention provides a modification to an area of interest visual display such that a low resolution image and a high resolution image are more easily blended in a manner which does not bring attention to an observer's eyes of a transition area between them.
2. The State of the Art
Area of interest display systems are typically utilized in simulators. The term "area of interest" refers to a section of a display which is of most interest and therefore watched by the observer. Typically, the most useful visual information is concentrated at this point, while a surrounding background image simply enhances a feeling of reality.
For example, a low resolution image is projected onto a display screen as background, while a high resolution image is combined with the low resolution image by being projected onto it. The high resolution image provides greater detail because it is a focal point of observational interest to the observer, hence it is the area of interest.
The high resolution image typically encompasses a small field-of-view and is inset into a wide field-of-view low resolution image. Consider a trainee who is seated in a flight simulator and observes a wide field-of-view display to simulate a view of an actual flight pattern. A trainee can therefore experience specific flight routes or patterns with considerable realism while seated in the training simulator.
It has been learned that as a result of limitations in human visual perception that a considerable portion of a wide field-of-view display may be of relatively poor quality and still attain substantial realism for the viewer. The key is to inset a high resolution image in the low resolution background image at the viewer's area of interest. Such area of interest systems take advantage of the high resolution viewing area of the eye (the fovea) being relatively small. Specifically, as the fovea of a normal eye subtends an angle of only about two degrees, the high resolution inset image can be relatively small in relation to the low resolution background or panoramic image.
A previously recognized problem in producing area of interest displays has been avoiding visible effects at a border between the low resolution and the high resolution images. Considerable effort has been expended in attempting to avoid incongruities that are disturbing and/or distracting to the viewer and which appear at the transition from the high resolution image to the low resolution image.
Although various solutions have been proposed to provide a visually acceptable transition between the images in an area of interest display, a need exists for an economical and effective process and apparatus to accomplish that end. In that regard, it is desirable to avoid the need for high precision optical alignment, exotic filtering or video systems requiring extensive hardware or critical operating requirements. In a related context, it is noteworthy that state of the art techniques presently suffer from substantial problems in attaining optical masks using proper sizing and proper optical density falloff.
To enhance the understanding of the state of the art which uses the techniques described above, FIG. 1 shows a system described in U.S. Pat. No. 5,326,266 issued to Fisher et al. (the '266 patent) which attempted to solve the problems of state of the art area of interest systems. The system 2 projects a composite picture on a view screen 8. A wide field, low resolution background image area 6 is indicated surrounding a high resolution inset area 4. The low resolution background image area 6 is generated by a background projector 5, while the high resolution inset area 4 is generated by a detail inset projector 7.
This system attempted to blend the images 4 and 6 at the view screen 8 by causing the border between the two areas 4 and 6 to vary in an orbital oscillating pattern to accomplish visual blending. Visual blending requires that a reflector plate 3 includes a transparent portion and an opaque portion, where the opaque portion reflects the inset area 4. The reflector plate 3 in this case is located at an intermediate image plane. Thus, one plate (the reflector plate 3) is used for both the background image and the inset image. The reflector plate 3 is then oscillated in the orbital pattern. This vibration is caused by an electro mechanical vibration drive 9 which is shown near the reflector plate 3.
FIG. 2 shows another state of the art system for creating a high resolution area of interest which is superimposed upon a lower resolution background display. In U.S. Pat. No. 4,634,384 issued to Neves et al. (the '384 patent), the system 20 uses a common servo optical arrangement for blending the inset area of interest with the background imagery. FIG. 2 shows that this system 20 uses beamsplitters 22 and multiple opaque filters 24 in the servo optical system. Accordingly, this system is disadvantageously complex and physically large in its implementation. This is partly due to the blend filters being specific to each channel, resulting in more filters being required. Furthermore, each filter must complement the filter in the other channel, even though the channels are physically separate from each other.